Stoichiometric transition metal hydrides



United States Patent 3,376,107 STOICHIOMETRIC TRANSITION METAL HYDRIDES Akira Oka, 71 Sugamo l-chome, Toshima-ku, Tokyo, Japan No Drawing. Filed May 15, 1964, Ser. No. 367,843 Claims priority, application Japan, May 20, 1963,

38/25,289; Oct. 10, 1963, 38/52,715; Jan. 31, 1964, 39/4,410; Feb. 18, 1%4, 39/8,362; Feb. 21, 1964, 39/ 9,028

1 Claim. (Cl. 23-204) ABSTRACT OF THE DISCLOSURE This invention relates to stable stoichiometric hydrides of metals of lV-B group of the periodic table and preparation method thereof and utilization thereof in the powder metallurgical process.

The object of this invention is to provide a rapid and economical process of producing stable stoichiometric IV-B metal hydrides.

One utilization of this invention is to provide an ultrafine powder of IV-B metal hydrides and IV-B metals.

Another utilization of this invention is to provide a simple and economical method of producing an nonporous sintered metal.

Another utilization of this invention is to provide a process for preparing single crystals of transition metals.

Another utilization of this invention is to provide a rapid and economical method of producing non-porous sintered alloys of varying compositions.

Another utilization of this invention is to provide chemically inert metallic receptacles by the process of depositing a stable IV-B metal on the surface of less eX- pensive metals.

Another utilization of this invention is to provide a simple methods to prepare cermets of any IV-B metal.

The success of this invention depends upon a new theory concerning the phenomenon that stoichiometric transition metal hydrides exist in a state which is very stable against air oxidation at room temperature, and they behave differently from powdered metals in the sintering process. Metallic bonding of great strength acts between activated titanium atoms produced by thermal decomposition of metallic hydrides, and a non-porous sintered material is obtained. On the other hand, in a case of ordinary powder metallurgical process using metal powder, a sintering process is interfered with a thin oxide film on a surface of the metal powder.

The published literature concerning the IV-B metal hydrides does not provide very precise information concerning their true structure. For instance, Moellor stated in his Inorganic Chemistry, The quantity of hydrogen present ordinarily bears no exact stoichiometric relation to the metal, and formulas such as TiH and TaH which are often given, probably represent no more than the conditions esential to saturation of the metal with hydrogen. R. P. Gibb stated in his paper (J. Electrochem. Soc. 93 198 (1948) Transition metal hydrides are structural complexities between interrnetallic and interstitial compound. Hansen summarised the available information concerning titanium hydride, and stated, There is complicating experimental evidence whether the homegeneity range of 7 phase extends nearly or wholly up to the composition TiH or whether even a distinct TiH exists, R. P. Gibb and W. Kruschwitz claimed the preparation of stoichiometric TiH which they report to be unstable below 400 C. And Gibb stated, Whether this limiting composition is properly called a compound 3,376,107 Patented Apr. 2, 1968 is debatable. There is unequivocal evidence that its composition and gross properties are definite and reproducible and that its X-ray diffraction pattern contains moderately strong lines not hitherto reported in the titanium-hydrogen system. These novel lines are two in number (d=2.076 A, 1.801 A) and are observable only for freshly prepared materials and are found to disappear gradually as the hydride is stored over a period of a few weeks in air.

The titanium, zirconium, hafnium hydride which the inventor prepared by heating high purity commercial sponge titanium, zirconium, hafnium with high purity hydrogen, obtained by passing the hydrogen through a Pd alloy membrane (U.S.P. 2,773,561) at atmospheric pressure is stoichiometric in composition and stable in air. The X-ray difiraction pattern showed no change over a two week period after it was produced. Titanium hydride which was powdered under atmospheric conditions in a mechanical agate mortar did not change its X-ray diffraction pattern except that some line broading occured. Stoichiometric titanium hydride is not pyrophoric although, it was found that the powdered titanium metal produced by thermal decomposition of the titanium hydride at 500 C. and a pressure of 10- mm. Hg is strongly pyrophoric. So fine powder of titanium hydride thus obtained is more stable against air oxidation than fine powder of metal.

The hydrogenation process was accomplished in a few minutes at atmospheric pressure in contrast to the cominercial process which is carried out at low pressure for a period of 30 hours.

The stability against air oxidation of stoichiornetric titanium hydride and the activated state of the metal produced by thermal decomposition of the hydride and sintering of the resultant titanium metal powder, make it possible to produce high grade titanium metal without the necessity of heating titanium to its melting point.

Many powdered metals have oxide surface which inter feres with the sintering process. Stoichiometric 1V-B metal hydrides are not subject to this source of interference and when thermal decomposition in vacuo occurs, titanium atom combines each other by excellent metallic bonding, and a sintered specimen is obtained.

Upon annealing this specimen, microcrystalline of titanium is produced which grows to a large single crystal.

All of the above-mentioned characteristics of stoichiometric IVB metal hydrides make it possible to prepare non-porous alloys of varying composition without the necessity of melting any of the components of the alloys.

Fine powders of transition metal hydrides were mixed, pressed and moulded. After dehydrogenation at temperature higher than 500 C. at a pressure of 5 10 mm. Hg, the specimen was heated at sintering temperature for two hours, and a non-porous alloy was obtained. When a mixture of hydn'de powder and metal powder were treated similarly, a non-porous alloy was also obtained. Metal hydrides at high temperatures have a strong reducing power which causes reduction of oxide film of metal surface.

All of the above mentioned factors make it possible to apply titanium and other IV-B metals as coating on steel surface. A fine powder of titanium and 5% of camphor by weight were dispersed in methyl alcohol and the sus pension was painted or sprayed on a clean surface of steel. After thermal decomposition in vacuo, it is heated at 1200" C. for 3 hours, and a complete non-porous coating of titanium was obtained.

This specimen was unaffected when kept in contact with 0.5 N HCl for two days. A tantalum coating prepared in the same manner was unaffected when kept in contact with 2 N HCl for two days. Chemical apparatuses for handling acid solution can thus be economically fabricated. Titanium is chemically stable against sea water, so titanium-coated steel pipe can be safely used in contact with sea water.

In addition wall of the above-mentioned factors, a nature of fine powder of stoichiometric transition metal hydride to make a eutectic with a metal surface, make it possible to bond materials. Steel and copper can adhere by a thin paste of titanium hydride at 950 C.

Cermets can combine using stoichiometric IV-B metal hydride without melting any component of the system. This fact can compare with an ordinary bonding using cobalt, which melts upon sintering.

EXAMPLE 1 Preparation of stoichiometric IV-B metal hydride. About 510 g. of a commercial purity sponge titanium (99.9%), was outgassed by heating at 800 C. under vacuum of 5x10 mm. Hg, then cooled to 450 C. and

a high purity hydrogen, obtained by passing the hydrogen were obtained. Larger quantity of hydrides was prepared as follows. About 150 g. of commercial purity sponge titanium (99.9%) was outgassed in the same manner as above. Using a hydrogen purifier of 1 m. hour capacity, and stoichiometric titanium hydride was obtained.

EXAMPLE 2 Production of stoichiometric titanium hydride using titanium as a gettering agent for the purificaton of hydrogen.

Sponge titanium was heated higher than 850 C. in vacuo and cylinder hydrogen hydrogen was passed over a layer of sponge titanium (-l mesh), which absorbed impurities in hydrogen (water vapour, oxygen, and nitrogen), and another layer of sponge titanium which was situated some distance under the gettering titanium layer absorbed purified hydrogen to form hydride of a stoichiometric composition.

The stoichiometric IV-B metal hydrides obtained by the above examples had the same FCC X-ray diffraction pattern, and the X-ray diffraction pattern did not change over a period of several weeks as did the X-ray diffraction pattern of R. P. Gibb as mentioned earlier. It is, therefore, true that this is the first preparation of a stable stoichiometric 1VB metal hydride.

EXAMPLE 3 Preparation of fine powder of stoichiometric IV-B metal hydrides and fine powder of said metals.

Powder of stoichiometric titanium hydride was obtained from the stoichiometric titanium hydride produced by the above-mentioned process by pulverizing it with a mechanical agate mortar for a week. During this process colloidal fine particles entered atmosphere and were colleoted by an electric precipitator. Such fine powder has been made by the invention for the first time.

The above-mentioned fine powder of stoichiornetric titanium hydride was heated higher than 500 C. in a vacuum of 5x10" mm. Hg, and a fine powder of titanium was obtained. This titanium powder is pyrophoric.

EXAMPLE 4 Preparation of a non-porous sintered specimen. Stoichiometric titanium hydride, of a mean diameter of 3 was pressed into a plate of 11.3 mm. diameter under a pressure of 5 t0I1S/CIIL It was then heated higher than its decomposition temperature under a vacuum of 5x10 mm. Hg. Then the activated titanium was sintered at 1200 C. for 2 hours and allowed to cool. The sintered plate which was prepared by this process had no porosity and its density was 4.52 approximately. This is the first non-porous sintered titanium.

EXAMPLE 5 Preparation of a single crystal of titanium.

Using the powder of titanium hydride prepared as above, a plate of 50 x 25 x 3 mm. was prepared using the same pressure, and the non-porous plate was obtained by the same sintering process which was shown to be microcrystalline titanium. After annealing process at 1250 C. for 2.5 hours and cooling over a night, it was revealed that the plate consisted of 4 single crystals of titanium.

EXAMPLE 6 Preparation of non-porous alloys by sintering of stoichiometric metal hydrides.

Mixed 0.6 g. of fine powder of stoichiometric titanium hydride and 0.6 g. of fine powder of stoichiometric zirconium hydride with an agate mortar for one hour. Pressed into a pellet of 11.3 mm. diameter by a pressure of 6 tons/om. Dlehydrogenated in a vacuum of 10- mm. Hg at 800 C. Sintered at 1250 C. for 2 hours. And a non-porous alloy was obtained.

EXAMPLE 7 Preparation of alloys by sintering of stoiehiometric IVb metal hydride and metal powder.

One gram (1 g.) of fine powder of stoichiometric zirconium hydride and 0.2 g. of molybdenum powder (200 mesh) were mixed by an agate mortar. The mixture was treated in the same manner as in Example 6, and a non-porous alloy was obtained.

EXAMPLE 8 Metal coating prepared by using stoichiometric titanium hydride and tantalum hydride.

The fine powder of titanium hydride mentioned above was dispersed in methyl alcohol containing camphor and painted on a clear surface of a steel rod (carbon content 0.15%). The rod was then heated in vacuo higher than 500 C. for dehydrogenation. The rod was then heated at 1200 C. for 3 hours under a vacuum of 5 l0 mm. Hg. A titanium-coated steel rod was obtained. The rod was immersed in 0.5 N HCl for two days, no effect on the rod was noted, while an identical steel rod without coating which was immersed in the same solution lost 50 mg. in weight.

EXAMPLE 9 Adhesion of metals using stoichiometric titanium hydride.

A sandwich arrangement was made by a plate of stainless steel, a thin paste of titanium hydride powder dispersed in methyl alcohol and a plate of copper. This specimen was pressed by a clamp, then heated at 950 C. under a vacuum of 5 10- mm. Hg for 2 hours, and an excellent bond which showed no change upon strong heating with a gas burner was obtained.

EXAMPLE 10 Preparation of cermets using stoichiometric titanium hydride. Mixed 0.5 g. tungsten carbide and 0.5 g. of fine powder of stoichiometric titanium hydride with an agate mortar, pressed into a pellet of 11.3 mm. diameter by pressure of 5 tons/cnr Dehydrogenated in a vacuum of 5 10 mm. Hg at 600 C., sintered at 1200 C. for References Cited an hour. And a sintered piece is obtained without melt- UNITED STATES PATENTS ing any component of the pellet.

What I claim is: 1,816,830 8/1931 Driggs 23-204 X 1. Process for preparing stable metal hydrides of metals 5 2452139 /1948 F of Group IV-B having the general formula MeH Where 2536510 1/1951 Klng 6! 23-210 X Me stands for a IV-B metal comprising the steps of: 3:152'868 10/1964 Kempter et 0 (I) purifying hydrogen by passing it thru a Pd alloy 1,120,561 12/1914 Strong et al 552 membrane with a dew point of -70 C, t one 2,495,761 950 Platt 156-157 atmosphere pressure to obtain high purity hydrogen; 10 2,994,606 8/ 1 Goodzeit 75214 (II) providing in a reaction zone a high purity sponge 072,499 1/ 1963 C016 et a1. 117130 metal of -10 mesh selected from the group consist- 3,107,175 /1963 Cape 117-130 ing of Ti at 99.99%, Zr at 99.6%, and Hf at 99.3%, 3,111,441 1 63 G undel 156-157 Said sponge being divided into a first gettering layer 3,116,112 12/1963 Jenkner 23204 and a second layer spaced from and underneath said 33144357 8/1964 Hulme et 1 1-6 gttering l 3,150,975 9/1964 Beaver et a1. 75-214 (III) outgassing said sponge metal by heating it to at 3,152,868 10/1964 Kgmptef 61581 23204 least 800 C. under a vacuum; 3,165,397 1 1965 LObO 75-O.5 (IV) cooling said sponge metal heated by the previous 3,136,829 6/1965 Landgraf 75-0.5 step to about 450 C. While maintaining the vacuum; 3,186,880 6/1965 skaggs et 1- (V) directing said purified hydrogen thru said sponge OTHER REFERENCES metal in the reaction zone while maintaining said atmospheric pressure and the temperature of about Ellis, Hydrogenation of Organic Substances, 3rd ed1- 450 C., whereby the first layer absorbs gaseous im- 9 purities from the hydrogen and the purified hydro- Hurd, chemlstry 0f the Hydrldes, 1952, pp. 181- gen emerging therefrom passes thru the second layer to form a stable stoichiometric hydride: of titanium, Pascal, Noveau Tfalte C me Mmerale, January having a formula in the range of lssBzio-Oosa V01. 9, pp.

of zirconium, having a formula in the range of MILTON WEISSM AN Primary Examiner 1.994:l;O.0022' and of hafnium, having a formula in the range of LEON ROSDOL OSCAR VERTIZ, Examlnel'szms R. L. GRUDZIECKI, Assistant Examiner. 

